Researchers at Tulane University tracked 148 obese men and women between the ages of 22 and 75 for one year. None of the participants had heart disease or diabetes. Half were randomly assigned to follow a low-carbohydrate diet for a year, and the other half were assigned to a low-fat diet for a year. They were told to not change their physical activity throughout the trial. The only difference between the groups was the proportions of carbohydrate and fat in their diets. Those in the low-carbohydrate group were told to eat at no more than 40 grams of digestible carbohydrates per day. Those in the low-fat group were told not to get more than 30 percent of their daily energy from fat and no more than 55 percent of their daily energy from carbohydrates. The low-fat dieters tried especially to limit saturated fatty acids (<7% saturated fat). Overall, about four of every five participants were still following the diets 12 months later.
Researchers found that people on the low-carbohydrate diet lost more weight and more body fat than those on the low-fat diet. The difference in lost weight between the two groups would represent about 3,5 kilogram. Additionally, a low-carb diet resulted in greater improvements in body composition, HDL cholesterol level, ratio of total/ HDL cholesterol, triglyceride level, C-reactive protein level, and estimated 10-year CHD risk. The researchers found no increases in total cholesterol and LDL cholesterol between the two groups. Generally, the overall diets improved among the participants and they were encouraged to eat healthier forms of protein like fish, nuts and beans.
The authors of the study conclude that restricting carbohydrates may be an option for persons who are seeking to lose weight and reduce cardiovascular risk factors. The researchers were not sure why people on the low-carbohydrate diets lost more weight and had lower risk factors for heart disease after one year. Furthermore, it is not clear if there would be still a difference between the two groups after a longer period than 12 months. What matters is that the individual can stick to the diet over the long term. This is still subject of much research.